1. Field of the Invention
The present invention relates to an electric oil pump that can greatly improve the operation, increase the endurance, and extend the service life of an Oldham's coupling connecting a drive shaft that rotates a rotor in a pump housing and a motor output shaft in a motor housing.
2. Description of the Related Art
Electric oil pumps comprising a combination of a pump housing having a drive shaft provided with a rotor of an inner contact gear type and a motor housing having a motor for rotating the drive shaft mounted on the rotor have been used as pumps in lubrication systems of automobiles or the like. A specific example of such electric oil pump is described in Japanese Patent Application Laid-open No. H11-173278. The essence of the invention disclosed in this application is that a hydraulic gear pump and a motor are connected via a bracket. A drive shaft on the side of the hydraulic gear pump and a rotor shaft on the side of the motor are connected via a coupling, and an Oldham's coupling is disclosed as an example of the coupling.
The construction of the Oldham' coupling disclosed in Japanese Patent Application Laid-open No. H11-173278 enables the rotation transfer even when the input shaft and output shaft are not coaxial. A plate-shaped protrusion is formed on the distal end of the output shaft of the motor, and a groove for inserting the protrusion is formed on the input shaft side of the pump housing. The output shaft of the motor rotates and the rotor shaft rotates in a state where the plate shaped protrusion is inserted into the groove. In this case, the rotation is transferred even though the input shaft and output shaft are not coaxial, but the plate-shaped protrusion and the groove rub against each other and the surfaces thereof wear each other in long-term usage, thereby decreasing the strength of the coupling. It is an object of the present invention to increase the endurance and extend the service life of the Oldham's coupling connecting the output shaft and input shaft.